The present invention relates generally to hot melt adhesive dispensing systems, and more particularly to a new and improved hot melt adhesive dispensing system which comprises a multiple-outlet metering gear pump for supplying hot melt adhesive to a plurality of snuffback-diversion flow valves, and wherein the system further comprises the use of a single return metering gear pump disposed within a return loop fluidically interconnecting the plurality of snuffback-diversion flow valves to the multiple-outlet metering gear pump such that inconsistent dispensing or bursting of the hot melt adhesive, characteristically present upon the commencement of a hot melt adhesive dispensing operation or cycle, is essentially eliminated, and in addition, quick shutoff, and proper pressure and volumetric control, of the adhesive supply internally within the valve assembly is able to be achieved at the termination of a hot melt adhesive dispensing operation or cycle, and particularly during the closure of the snuffback valve, such that the undesirable stringing of the adhesive does not occur within such a multiple-outlet metering gear pump system.
In connection with the dispensing of highly-viscous materials, such as, for example, hot melt adhesives, it is imperative that the dispensing system comprise what is known in the art as a snuffback valve by means of which the shutoff or termination of the dispensed adhesive is readily achieved upon closure of the valve whereby stringing of the adhesive does not occur. As disclosed within the aforenoted previously filed patent application, U.S. patent application Ser. No. 09/550,884, prior art snuffback valves, while certainly being capable of substantially performing their basic operations of controlling and preventing the dispensing of hot melt adhesives, nevertheless suffered several operational drawbacks or disadvantages, such as, for example, being relatively slow-acting, and permitting the aforenoted undesirable stringing of the hot melt adhesive materials upon termination of a hot melt adhesive dispensing cycle. In addition, due to the particular structural characteristics of such conventional or prior art snuffback valves, the dispensing systems would also experience or exhibit a phenomenon known as bursting wherein, upon commencement of a new adhesive dispensing operation or cycle, a sudden expulsion, discharge, or dispensing of a predetermined amount or glob of adhesive would occur.
Accordingly, by means of the particularly new and novel structure of the snuffback valve as disclosed within the aforenoted previously filed patent application, U.S. patent application Ser. No. 09/550,884, the aforenoted operational problems, drawbacks, and disadvantages characteristic of the conventional or prior art snuffback valves have been addressed and have been substantially reduced or rectified. It was determined still further, however, that some of the aforenoted problems characteristic of the prior art snuffback valves, such as, for example, bursting and stringing, nevertheless persisted to some degree within current hot melt adhesive dispensing systems despite the structural improvements, modifications, and refinements made to the snuffback valves in accordance with the teachings and principles of the invention embodiments as disclosed within the previously filed patent application, U.S. patent application Ser. No. 09/550,884. The reason for this is that the problems or operational drawbacks or disadvantages were no longer based or founded upon structural characteristics of the snuffback valve per se, but to the contrary, were believed to be based upon, or caused by, pressure and volumetric parameters characteristic of the hot melt adhesive dispensing system per se.
Accordingly, by means of the new and improved combination diversion-snuffback flow valve system disclosed within the aforenoted U.S. patent application Ser. No. 09/550,884 filed on Apr. 17, 2000 , a diversion valve was integrally incorporated into the snuffback valve system wherein the pressure and volumetric parameters of the valve system were able to be advantageously predetermined and controlled such that the valve mechanism was rendered relatively fast-acting, and wherein further, bursting and stringing of the hot melt adhesive materials, upon commencement and termination of a particular hot melt adhesive dispensing operation or cycle, were respectively prevented or significantly reduced. It is noted, however, that the system disclosed within the aforenoted U.S. patent application Ser. No. 09/550,884 filed on Apr. 17, 2000 comprises what is known in the art as a pressurized hot melt adhesive dispensing system, however, hot melt adhesive dispensing systems may also comprise what is known in the art as a metered output hot melt adhesive dispensing system. During the operation of such metered output hot melt adhesive dispensing systems, in a manner similar to the operation of pressurized hot melt adhesive dispensing systems, it is often imperative or desired to cycle the dispensing of the adhesive material output from the gearhead in ON and OFF modes by suitably actuating the combination diversion-snuffback valve assemblies. Accordingly, it is likewise imperative that, in conjunction with the operational cycling of such metered output hot melt adhesive dispensing systems, the aforenoted dispensing problems comprising stringing and bursting must likewise be addressed and rectified whereby such metered output hot melt adhesive dispensing systems will not exhibit undesirable stringing and bursting characteristics.
Accordingly, a need exists in the art for a new and improved metered output hot melt adhesive dispensing system wherein the pressure and volumetric parameters can be advantageously predetermined and controlled such that the undesirable phenomena of bursting and stringing of the hot melt adhesive materials, upon commencement and termination of hot melt adhesive dispensing operations or cycles in accordance with the ON and OFF or OPEN and CLOSED modes of the combination snuff-back-diversion flow valves, are respectively prevented or significantly reduced.
Accordingly, it is an object of the present invention to provide a new and improved metered output hot melt adhesive dispensing system.
Another object of the present invention is to provide a new and improved metered output hot melt adhesive dispensing system which effectively overcomes the various operational disadvantages and drawbacks characteristic of conventional or prior art metered output hot melt adhesive dispensing systems.
An additional object of the present invention is to provide a new and improved metered output hot melt adhesive dispensing system which effectively overcomes the various operational disadvantages and drawbacks characteristic of conventional or prior art metered output hot melt adhesive dispensing systems by the inclusion, within a metered output hot melt adhesive dispensing system comprising a multiple-output metering gear pump which supplies hot melt adhesive material to a plurality of combination snuffback-diversion flow valves, of a return loop which has a single return metered output gear pump disposed therein for with-drawing a predetermined volumetric amount of hot melt adhesive material from the snuffback-diversion flow valves when one or more of the snuffback-diversion flow valves is disposed in its non-discharging or non-dispensing OFF mode so as to relieve back-pressure or pressure buildup parameters with respect to the snuffback-diversion flow valves.
A further object of the present invention is to provide a new and improved metered output hot melt adhesive dispensing system which effectively overcomes the various operational disadvantages and drawbacks characteristic of conventional or prior art metered output hot melt adhesive dispensing systems by the inclusion, within a metered output hot melt adhesive dispensing system comprising a multiple-output metering gear pump which supplies hot melt adhesive material to a plurality of combination snuffback-diversion flow valves, of a return loop which has a single return metered output gear pump disposed therein for withdrawing a predetermined volumetric amount of hot melt adhesive material from the snuffback-diversion flow valves when one or more of the snuffback-diversion flow valves is disposed in its non-discharging or non-dispensing OFF mode so as to relieve back-pressure or pressure buildup parameters with respect to the snuffback-diversion flow valves such that the phenomena of stringing and bursting do not occur, or are significantly reduced, when the snuffback-diversion flow valves are operationally cycled in accordance with intermittently actuated ON and OFF states or modes of operation.
The foregoing and other objectives are achieved in accordance with the teachings and principles of the present invention through the provision of a new and improved metered output hot melt adhesive dispensing system which comprises a multiple outlet metering gear pump which supplies hot melt adhesive material to a plurality of snuffback-diversion flow valves through means of a laminated gear head, and wherein further, there is provided a return loop fluidically connecting the plurality of snuffback-diversion flow valves back to the inlet side of the multiple outlet gear pump. A single return metering gear pump is disposed within the return loop, and the single return metering gear pump has a check-valve controlled recirculation loop fluidically connected thereto such that the recirculation loop fluidically connects the inlet and outlet sides of the single return metering gear pump. In this manner, significant back-pressure or pressure-buildup parameters upon the upstream or non-dispensing ends of the snuffback-diversion flow valves are effectively relieved or eliminated so as to effectively prevent or eliminate the phenomena of bursting and stringing as the snuffback-diversion flow valves are operationally cycled in accordance with intermittently actuated ON and OFF or OPEN and CLOSED states or modes of operation.